The invention relates to a method and an apparatus for the continuous production of standardized milk having a predetermined fat content from raw milk of higher fat content, in which the rate of flow of the cream flowing from a cream separating centrifuge and being remixed with the skim milk is regulated in accordance with the fat content of the standardized milk, and the excess cream is carried off separately.
A method of this kind is known from Westfalia publication No. 2315/466 "Reinigung und Standardisierung von Milch mit Westfalia Doppelgreifer-Separatoren".
In this known method, the raw milk as supplied, with a higher constant fat content, is separated in a cream separating centrifuge into cream and skim milk and the portion of the cream that is needed for the fat content of the standardized whole milk is remixed with the skim milk by means of a system of piping and valves located outside of the centrifuge, and the excess cream is carried off separately.
The apparatus for the practice of the known method consists of a cream separating centrifuge to which the raw milk is delivered with a constant fat content, at a constant rate of flow through a flow limiter, and from which both the skim milk and the cream are pumped under pressure, by means of a paring disk for example, into its discharge lines.
For the purpose of maintaining the quantity ratio between the cream and the skim milk, a flow meter is installed in the cream discharge line, and in order to mix a portion of the cream with the skim milk, the two discharge lines are connected together by a branch line equipped with a regulating valve.
The rate of flow of the excess cream is measured by an additional flow meter and is adjusted with a cream control valve following the flow meter in the circuit.
The amount of cream to be carried off in the known method is calculated on the basis of the rate of flow and fat content of the raw milk input to the centrifuge, and of the fat content of the cream emerging from the centrifuge. The greater the number of fat units per unit of time that are fed to the centrifuge, the greater the number of fat units will be which must be withdrawn separatedly from the process. This means that not only must the rate of flow and fat content of the raw milk input be constant, but also the fat content of the cream and the amount of cream to be discharged separately must be precisely adjusted and held constant.
If, however, the fat content of the raw milk is variable, the methods known hitherto do not suffice for the production of standardized milk with a very precisely controlled fat content. In Germany, for example, the fat content of standardized whole milk must be at least 3.5% according to law, and it must not fall below this level. To exceed this fat content, however, represents a loss for the dairy, which for this reason desires to produce standarized milk with a very precisely controlled fat content.
If, for example, the fat content of standardized milk is to amount to 3.5%, a maximum fat content of 3.55% will be allowed by the dairy. Since the butterfat content must not, according to law, fall below 3.5%, the butterfat tolerance will amount to .+-. 0.025%. If, for example, 100,000 liters of milk are sold with 3.55% butterfat instead of 3.5% butterfat, the loss to the dairy will be 5,000 units of fat, corresponding to approximately 60 kg of butter.
In the centrifugal milk separators, the preset ratio of skim milk to cream and the fat content in the skim milk remain constant, even when the fat content of the cream varies. In this case, regulation through rate-of-flow measurement, as described in the beginning, is no longer possible.